1. 1 © 2006 Brooks/Cole - Thomson THREE STATES OF MATTER Draw particle models of the 3 states of matter. Describe the properties of the particles.

2. 2 © 2006 Brooks/Cole - Thomson Hot Air Balloons — How Do They Work? Describe how the particles change as the air is heated. Talk about volume, number of particles (this is the tricky part), and density.

3. 3 © 2006 Brooks/Cole - Thomson Importance of Gases Airbags fill with N 2 gas in an accident.Airbags fill with N 2 gas in an accident. Gas is generated by the decomposition of sodium azide, NaN 3.Gas is generated by the decomposition of sodium azide, NaN 3. 2 NaN 3 ---> 2 Na + 3 N 22 NaN 3 ---> 2 Na + 3 N 2 How much sodium azide is required to fill an air bag? (Assume it fills at 1 atm of pressure, 300 K, and to 60 L of volume.)How much sodium azide is required to fill an air bag? (Assume it fills at 1 atm of pressure, 300 K, and to 60 L of volume.) You will solve this later this week….You will solve this later this week….

4. 4 © 2006 Brooks/Cole - Thomson General Properties of Gases There is a lot of “free” space in a gas.There is a lot of “free” space in a gas. Gases can be expanded infinitely.Gases can be expanded infinitely. Gases occupy containers uniformly and completely.Gases occupy containers uniformly and completely. Gases diffuse and mix rapidly.Gases diffuse and mix rapidly.

5. 5 © 2006 Brooks/Cole - Thomson Properties of Gases Gas properties can be modeled using math. Model depends on— V = volume of the gas (L)V = volume of the gas (L) T = temperature (K)T = temperature (K) n = amount (moles)n = amount (moles) P = pressure (atmospheres)P = pressure (atmospheres)

6. 6 © 2006 Brooks/Cole - Thomson Pressure Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643) A cylinder has all air removed (vacuum) and is inverted into a pool of liquid mercury

7. 7 © 2006 Brooks/Cole - Thomson Pressure Hg rises in tube until force of Hg (down) balances the force of atmosphere (pushing up into the cylinder). How is this related to a drinking straw? P of Hg in column pushing down is related to Hg density (13.55 g/mL)Hg density (13.55 g/mL) column heightcolumn height

8. 8 © 2006 Brooks/Cole - Thomson Pressure Column height measures P of atmosphere 1 standard atm = 760 mm Hg1 standard atm = 760 mm Hg = 29.9 inches Hg = about 34 feet of water SI unit is PASCAL, Pa, where 1 atm = 101.325 kPa

9. 9 © 2006 Brooks/Cole - Thomson Atmospheric Pressure At different altitudes –14.7 lb/in 2 at sea level, 12.2 lb/in 2 in Denver at about 5,000 ft, 10.1 lb/in 2 in Breckenridge at about 10,000 ft. Atmospheric pressure cuts in half about every 15,000-20,000 ft above sea level. On a balloon On a can

10. 10 © 2006 Brooks/Cole - Thomson What is the difference between Boiling and Evaporation? Evaporation is a phase change from liquid to gas that takes place at the surface of the liquid. It occurs when random particles have enough energy to escape the intermolecular forces of attraction to the liquid at its surface.

11. 11 © 2006 Brooks/Cole - Thomson What is the difference between Boiling and Evaporation? Boiling is the rapid transition of liquid molecules to gas molecules that takes place at the bottom of the container (at the heat source), producing bubbles of the gaseous substances throughout the container, within the liquid substance, to rise to the top with enough energy to escape both the intermolecular forces and the force of atmospheric pressure. A liquid boils when its VAPOR PRESSURE equals ATMOSPHERIC PRESSURE.

12. 12 © 2006 Brooks/Cole - Thomson EXPLORE! Can you decrease the pressure in a bell jar to boil water at a temperature below 100 o C? What is the relationship between pressure and volume? Use a marshmallow or shaving cream inside a bell jar to explore this relationship. What is the relationship between number of particles and volume? Can you find a way to demonstrate this with a balloon? What is the relationship between temperature and volume? Attach your balloon to the top of a flask containing water on a hot plate. Do not allow balloon to fill too much, use tongs to remove it from hot plate when done. Check out the demo in the microwave….

13. 13 © 2006 Brooks/Cole - Thomson IDEAL GAS LAW Brings together gas properties. Can be derived from experiment and theory. P V = n R T Practice Problems to be Proficient in PVnRT!

14. 14 © 2006 Brooks/Cole - Thomson Combining the Gas Laws At Standard pressure and temperature (STP) T = 273 K P = 1.00 atm –What is the volume of 1.00 mol of a gas? V = 22.4 L This is called molar volume (at STP)

15. 15 © 2006 Brooks/Cole - Thomson Kinetic Molecular Theory Because we assume molecules are in motion, they have a kinetic energy. KE = (1/2)(mass)(speed) 2 At the same T, all gases have the same average KE. As T goes up for a gas, KE also increases — and so does speed. What does this mean about the speeds of gases with different masses at the same temperature…?

16. 16 © 2006 Brooks/Cole - Thomson KINETIC MOLECULAR THEORY (KMT) Theory used to explain gas laws. KMT assumptions are Gases consist of molecules in constant, random motion.Gases consist of molecules in constant, random motion. P arises from collisions with container walls.P arises from collisions with container walls. No attractive or repulsive forces between molecules. Collisions elastic.No attractive or repulsive forces between molecules. Collisions elastic. Volume of molecules is negligible.Volume of molecules is negligible.

17. 17 © 2006 Brooks/Cole - Thomson Deviations from Ideal Gas Law Real molecules have volume.Real molecules have volume. There are intermolecular forces.There are intermolecular forces. –Otherwise a gas could not become a liquid.

18. 18 © 2006 Brooks/Cole - Thomson Under what conditions do gases deviate from Ideal Conditions? Gases are LESS LIKE GASES when: –Pressure is HIGH –Temperature is LOW »Particles will be too close together in both instances, resulting in less gas-like conditions

19. 19 © 2006 Brooks/Cole - Thomson Deviations from Ideal Gas Law Account for volume of molecules and intermolecular forces with VAN DER WAALS’s EQUATION. Measured V = V(ideal) Measured P intermol. forces vol. correction J. van der Waals, 1837-1923, Professor of Physics, Amsterdam. Nobel Prize 1910. nRT V - nb V 2 n 2 a P + ----- )(

20. 20 © 2006 Brooks/Cole - Thomson Using PV = nRT Airbags fill with N 2 gas in an accident.Airbags fill with N 2 gas in an accident. Gas is generated by the decomposition of sodium azide, NaN 3.Gas is generated by the decomposition of sodium azide, NaN 3. 2 NaN 3 ---> 2 Na + 3 N 22 NaN 3 ---> 2 Na + 3 N 2 How much sodium azide is required to fill an air bag? (Assume it fills at 1 atm of pressure, 300 K, and to 60 L of volume.)How much sodium azide is required to fill an air bag? (Assume it fills at 1 atm of pressure, 300 K, and to 60 L of volume.)

21. 21 © 2006 Brooks/Cole - Thomson Using PV = nRT How much N 2 is req’d to fill an air bag with a volume of 60.0 L to P = 1 atm at 300 K? R = 0.082057 Latm/Kmol R = 0.082057 Latm/KmolSolution 1. Get all data into proper units 2. Solve for moles (n) 3. Solve for what you are looking for.

22. 22 © 2006 Brooks/Cole - Thomson Gases and Stoichiometry 2 H 2 O 2 (liq) ---> 2 H 2 O(g) + O 2 (g) Decompose 1.1 g of H 2 O 2 in a flask with a volume of 2.50 L. What is the pressure of O 2 at 25 o C? Of H 2 O? Bombardier beetle uses decomposition of hydrogen peroxide to defend itself.

23. 23 © 2006 Brooks/Cole - Thomson Gases and Stoichiometry 2 H 2 O 2 (liq) ---> 2 H 2 O(g) + O 2 (g) Decompose 1.1 g of H 2 O 2 in a flask with a volume of 2.50 L. What is the pressure of O 2 at 25 o C? Of H 2 O? Solution Strategy: Calculate moles of H 2 O 2 Use the coefficient ratio Finally, calc. P from n, R, T, and V.

24. 24 © 2006 Brooks/Cole - Thomson Gases and Stoichiometry 2 H 2 O 2 (liq) ---> 2 H 2 O(g) + O 2 (g) Decompose 1.1 g of H 2 O 2 in a flask with a volume of 2.50 L. What is the pressure of O 2 at 25 o C? Of H 2 O? Solution

25. 25 © 2006 Brooks/Cole - Thomson Gases and Stoichiometry 2 H 2 O 2 (liq) ---> 2 H 2 O(g) + O 2 (g) Decompose 1.1 g of H 2 O 2 in a flask with a volume of 2.50 L. What is the pressure of O 2 at 25 o C? Of H 2 O? Solution P of O 2 = 0.16 atm What is the P of H 2 O? Notice: There are twice as many moles of H 2 O 2 as there are moles of O 2. How does the pressure relate to the number of moles? What is the total number of moles in the flask? What is the total pressure in the flask?